This invention relates to a messaging system, in particular a messaging system for use in the DECT (Digital European Cordless Telecommunications) system and other communications systems such as WCPE (Wireless Customer Premises Equipment) and PHS (Personal Handyphone System). The system may be used to provide a multipurpose messaging service that can be used for access to alternate data/messaging services with a common air interface structure accomplished with a general protocol layer defined on the top of the DECT protocol layers.
One implementation of a DECT system will now be described.
The Digital European Cordless Telecommunications (DECT) is a standard provided for cordless communications for both voice and data traffic. Reference may be had to the ETSI documents defining the system, which are incorporated herein by reference. A DECT system includes at least one portable part (PP) and at least one fixed part (FP). The PP contains all elements between the user and the air interface whereas the FP contains all elements between a local network and air interface. Thus no fixed infrastructure has been defined. The connection to the networks is made through interworking unit (IWU), functions of which are defined in the DECT profiles.
The DECT protocol layer structure is illustrated in the FIG. 1. The following descriptions of the layers are based on the common interface standard ETS 300 175-1 to 9. Radio Equipment and Systems (RES); Digital European Cordless Telecommunications (DECT) Common interface Part 1-9. European Telecommunications Standards Institute 1992 thus the features described here form a library of services for use by different profiles. DECT provides on the physical layer, in the frequency band of 1880-1900 MHz, 10 carriers each of which are carrying 24 TDMA slots. The slots can be used for either bi-directional (12 slots for both directions) or unidirectional traffic (maximum of 23 slots for one direction). The gross bit rate is 1152 kbit/s. A timeslot is divided into control/signalling (4.8 kbit/s net rate) and traffic fields (32 kbit/s net rate).
The medium access layer (MAC) can provide broadcast, connectionless and connection oriented service. The connection oriented service can be non-protected or protected. The protected service provides a possibility for modulo 2 retransmisson.
The data link control layer is divided into C- (signalling and low rate user traffic) and U-planes (user traffic). The U-plane can provide the following services for the upper layer application: LU1 transparent unprotected data (for voice), LU2 frame relay (data), LU3 frame switching (LU2 with LAP protocol for data), LU4 forward error correction (data), LU5 and LU6 rate adaptation for V.110 traffic. In addition LU7 is defined in the DECT/ISDN interworking profile to provide services for ISDN traffic.
The network layer on the C-plane contains the following services: Call Control (CC) used for call establishment and maintenance, mobility management (MM), call independent supplementary service (CISS) used for supplementary services, connection oriented message service (COMS) is an acknowledgment service used for transportation of limited amount of user data and Connectionless message service (CLMS) used for broadcast or point to point connectionless traffic. Call related supplementary services (CRSS) are related to a CC call and it provides a specific keypad protocol for the service management. The U-plane does not have a network layer.
According to a first aspect of the present invention there is provided a messaging system for communicating a message between a first communications unit having a first messaging entity and a second communications unit having a second messaging entity, each messaging entity comprising: a messaging call control means for establishing a messaging communications link with the other messaging entity; and a messaging means for, once the messaging communications link has been established, exchanging messaging information with the said other messaging entity.
Preferably, the messaging entity constitutes a virtual layer between the application layer and the network layer of the communication protocol.
The messaging information suitably includes header data and user data associated with the message. The header data and the user data suitably include data defining a message sequence number of the message. The header data and the user data are preferably carried by different communications links. Most preferably one link operates through a C-plane and the other link operates through a U-plane of a communication protocol.
The messaging system suitably operates according to the DECT, WCPE or PHS protocols. One of the communications units may be a portable part and the other is a fixed part. Alternatively, one of the units may be an intermediate server unit. One of the communications units may be provided with an interworking unit for performing protocol conversion.
According to the present invention from a second aspect there is provided a messaging method for communicating a message between a first communications unit and a second communications unit, the first communications unit having an application layer, a messaging entity and a network layer, the method comprising the steps of: transmitting a signal from the application layer to the network layer as a means of establishing a call; exchanging messaging information between the application layer and the network layer by way of the messaging entity to communicate the message; and transmitting a signal from the application layer to the network layer as a means of disconnecting the call.
According to the present invention from a third aspect there is provided a messaging method for communicating a message between a first communications unit and a second communications unit, the first communications unit having an application layer, a messaging entity and a network layer, the method comprising the steps of: transmitting a signal from the messaging entity to the network layer as a means of establishing a call; exchanging messaging information between the application layer and the network layer by way of the messaging entity to communicate the message; and transmitting a signal from the messaging entity to the network layer as a means of disconnecting the call.
In the messaging system/method commands can preferably be sent between messaging entities of each communications unit. The commands preferably include MMS SEND, MMS RETREIVE, MMS-RETREIVE-RPY, MMS COMMAND, MMS-COMMAND-RPY and MMS STATUS.
A messaging entity can preferably request a reply from the other messaging entity or an end entity. The said header data is preferably conveyed in one or more DECT/WCPE/WLL call control information elements and most preferably in one CC message.
The messaging system/method preferably includes any or all aspects of the up/downgrading, the service negotiation and the interworking procedures and the  less than  less than BASIC-SERVICE greater than  greater than  element described below.
The present invention suitably relates to a system for, for instance, providing teleservices for FAX and short message (such as GSM SMS) transfer. This may suitably allow for GSM interworking and also, generally, may extend the capabilities of DECT systems. In the future the demand for data messaging may also expand to other teleservices/data services (such as Internet based messaging/file transfer) and the present invention may preferably provide for this too. Employing a preferred embodiment of the invention a DECT system may expand from a cordless telephone system into a multipurpose information system with a wide variety of information services. At the same time it may offer also basic voice traffic and hence widen the possibilities for DECT service providers and manufacturers.
The present invention suitably provides a messaging service for a DECT system which can provide a wide variety of network services with a single new protocol layer compared to prior art DECT systems. In this way a simple and cheap portable terminal with wide variety of messaging/data services may suitably be provided for users. The protocol preferably contains a general set of minimum functionality for all alternate services, because the services contain such a wide variety of different options that it may conceivably be difficult to accomplish all functions of different services at the same time while maintaining a low level of complexity of a protocol.
The new protocol layer will be referred to as a multipurpose messaging service (MMS). The MMS protocol may preferably provide for general interworking to multiple information services such as T.611 Fax, GSM SMS, CCITT X.400 and internet HTTP.
The protocol may preferably be usable by both short messaging and fax/file services. The principal difference between these type of services is in the transmission capability: the short messaging preferably uses only the control channel (C-plane) for MMS signalling and user data transfer whereas the fax/file service preferably uses the traffic channel (U-plane) for user data and control channel (C-plane) for MMS signalling. This type of structure can suitably provide a flexible service. That is, a U-plane bearer service (C.2 data profile) can suitably be upgraded into fax/file transfer-teleservice by adding the MMS protocol on it. Also short messaging (E profile) can suitably be upgraded to a fax service by adding the U-plane service to the short messaging. Downgrading is preferably also possible. These procedures can suitably be done during already established connection as illustrated in FIG. 2. This procedure can be utilized for instance by sending the user a short message indicating that a fax is arriving. The user can, if he is capable to receive the fax, upgrade his short message connection into a fax capable high speed service to receive the fax.
Since the prior art DECT air interface typically supports only a limited service negotiation capability, the present invention preferably also provides for a new flexible service negotiation, suitably by adding new elements to some DECT messages. In this way the service negotiation may suitably be more flexible and some interworking unit/network service parameters may suitably be negotiated/changed even during call establishment. Also a new coding of the DECT IWU selection ( less than  less than iwu-attributes  greater than  greater than ) element may preferably be used to provide more general coding to IWU service selection. This may help to overcome the problem that prior art DECT coding is only ISDN oriented and does not fit well into general data service selection. The new coding is preferably backwards compatible with the old coding.
Aspects of the present invention may help to provide the following advantages:
allowing a wide set of services to be accessed in a standardized simple way;
providing relatively simple terminal applications, so the terminals can be simple and cheap;
providing an up/down grading procedures allowing a user friendly flexible service system to be implemented;
allowing expansion of the DECT systems and terminals for future data services;
minimizing the changes required in the DECT protocol layers
keeping close to the GAP DECT general voice profile, reducing the changes required in standard DECT terminals
Processing aspects of the present invention may suitably be provided by appropriate software operating under the control of a processor in a fixed or portable part.